The present invention relates to a variable light attenuator for use with optical fibers, and more particularly to a variable light attenuator for use with a multiple-fiber ribbon wherein the optical power to be supplied to the multiple-fiber ribbon, consisting of a plurality of optical fibers arranged in parallel, can continuously be controlled.
FIG. 5 shows a conventional variable light attenuator for attenuating the light power transmitted through an optical fiber.
Rod lenses 44 and 45 are provided at the ends of optical fibers 41 and 42, respectively. A thin glass plate 43 is arranged in a space between rod lenses 44 and 45.
Glass plate 43 has an evaporated thin film made of a metal or the same type of material on one side thereof where the transparency continuously changes with distance in the vertical direction. The transparency can be changed if glass plate 43 is forcibly moved toward the arrows shown in the figure.
FIG. 6 is a cross-sectional view of another example of a conventional variable light attenuator.
Ferrules 48 and 49 are attached to first and second optical fibers 46 and 47 so that the ferrules 48 and 49 which face each other are inserted together into an alignment sleeve 50. The optical power passing through the variable light attenuator can be changed by changing distance S from the end of ferrule 48 to the end of ferrule 49.
As distance S increases, the light power from optical fiber 46 is scattered, and the light power at the end of optical fiber 47 decreases.
FIG. 7 shows the structure of a single-mode multiple-fiber ribbon consisting of a plurality of optical fibers.
Optical fiber element 51 is covered with a protective coating 52 to form an optical fiber element.
A multiple-fiber ribbon consists of four to 12 optical fiber elements arranged in a line.
The optical fiber element has an outer diameter of 0.125 mm, and four to 12 optical fiber elements are generally arranged with a pitch of 0.25 mm.
A variable light attenuator for use with a multiple-fiber ribbon consisting of a plurality of optical fibers is being developed. However, the structure of FIG. 5 or FIG. 6 cannot be employed.
The end of a first optical fiber is separated from the end of a second optical fiber in the conventional variable light attenuator. If the light power from a plurality of optical fibers arranged in a line with 0.25 mm spacings is input to a variable light attenuator whose optical paths are arranged in line with 0.25 mm spacings, the optical signals from different optical fiber elements interfere with each other in the space where attenuation occurs. An optical signal in an optical fiber is partly transmitted to the adjacent optical fiber in the other line after passing through a variable light attenuator of this type, causing crosstalk in the adjacent optical fiber.
FIG. 8 shows the structure of an example of an optical switch for a multiple-fiber ribbon comprising optical fibers originally presented by the inventor of the present invention, and which is not prior art.
Either circuit "B" or "C" is selected by a solenoid of the switch shown in FIG. 8.
Ferrule assemblies 53 through 55 are provided to connect multiple-fiber ribbon "A" to multiple-fiber ribbon "B" or "C". Ferrule assemblies 54 and 55 are fastened to a substrate (not shown) so that ferrules 54 and 55 are arranged in parallel, so that ferrule assembly 53 is arranged to face toward ferrule 54 or 55.
A first electromagnetic actuator consisting of a movable iron core 56 and solenoid coil 57 is provided on one side of ferrule assembly 53. A second electromagnetic actuator consisting of a movable iron core 58 and solenoid coil 59 is provided on the other side of ferrule assembly 53.
Movable iron cores 56 and 58 alternately strike ferrule assembly 53 when a current flows through solenoid coils 57 and 59 alternately. When movable iron core 56 strikes ferrule assembly 53, ferrule assembly 53 goes to the position of ferrule assembly 55 immediately. When movable iron core 58 strikes ferrule assembly 53, ferrule assembly 53 goes to the position of ferrule assembly 54 immediately. When ferrule assembly 53 is set at the position of ferrule assembly 55, circuit "A" is connected to circuit "C". When ferrule assembly 53 is set at the position of ferrule assembly 54, circuit "A" is connected to circuit "B".
A DC current always flows through one of solenoid coils 57 and 59 during operation, and a temperature rise within each solenoid coil expands the respective parts therein. This expansion reduces the long-term stability and reliability of the attenuator.
The objective of the present invention is to present a variable light attenuator for use with a multiple-fiber ribbon consisting of a plurality of optical fibers arranged in a line which is, with long-term stability and reliability, used to continuously attenuate optical power to an appropriate amount in the 0 to 100% range and used to cut off the optical power as an optical switch.